Dual voltage engine starter systems have been known heretofore. For example, J. E. Coughlin U.S. Pat. No. 2,895,057, dated July 14, 1959, discloses an automatic switching apparatus whereby two 6-volt batteries may be automatically and temporarily switched from parallel connection to series connection for automobile starting purposes while simultaneously excluding other devices which are normally supplied with current by the batteries from receiving such boosted voltage during the starting interval. Also, J. W. Lee U.S. Pat. No. 3,871,383, dated Mar. 18, 1975, relates to a power supply system having two parallel connected batteries and includes circuit means responsive to the voltage across the output terminals of this power supply falling to a predetermined value for automatically connecting the batteries in series. While these dual voltage systems have been useful for their intended purposes, this invention relates to improvements thereover.